Crystalline particles such as RCS are a major occupational health and safety issue in industries such as mining, sandblasting, foundry work, agriculture, and construction. Minute shard-like particles of RCS (or other crystalline particles) can be carried in air currents for considerable distances and, if inhaled, are small enough to enter the deepest parts of the lung (alveoli) where they can become trapped. The resistance of crystalline particles to the body's attempts to remove them or chemically break them down means that they remain in the lungs for considerable periods, during which time they continue to cause irritation and damage.
Eric J. Esswein et al., (Eric J. Esswein, Michael Breitenstein, John Snawder, Max Kiefer and W. Karl Sieber, Journal of Occupational and Environmental Hygiene, 10: 347-356, 2013), describes a previously unreported occupational health hazard, that of worker exposure to RCS during hydraulic fracturing, or ‘fracking’, to extract shale gas and oil. Fracking operations have in recent times seen substantial and rapid expansion and have raised new concerns over the release of RCS into the atmosphere around fracking sites and the consequent potential for not only worker exposure but also, because of the proximity of many sites to residential areas, members of the general public.
Fracking involves high pressure injection of large volumes of water and sand, and smaller quantities of well treatment chemicals, into a gas or oil well to fracture shale or other rock formations, allowing more efficient recovery of hydrocarbons from a petroleum-bearing reservoir. Crystalline silica (quartz), also known as frac-sand, is a hard material commonly used in the operations to hold open cracks and fissures created by hydraulic pressure.
Each stage of the fracking process requires many tonnes of quartz-containing sand, and this may be repeated many times over the geographic extent of the reservoir. The generation of RCS may occur throughout the fracking process, from the initial delivery of the bulk fracking sand by road or rail, through to the mechanical unloading and storage of the fracking sand, and to the ultimate mixing of the sand with water and treatment chemicals. RCS is a significant health hazard if inhaled, and can cause health problems such as silicosis of the lungs and a variety of other life threatening conditions.
Current methods of monitoring the amount of RCS in the atmosphere rely on its collection through a fine-pore filter over a sampling period of hours or days. The filter is then carefully removed, packaged, and shipped to an external laboratory for gravimetric analysis and analysis via optical microscopy and/or X-ray crystallography analysis to determine the quantity of RCS that may be present. Knowledge of the volume of air that had been drawn through the filter then allows an estimate of the mass per unit volume of RCS that had been present in the vicinity of the filter unit over the course of the sampling.
However, this process has two significant disadvantages: Firstly, the time taken to collect, ship, and analyse the filter sample is typically days, during which time potential exposure of personnel is continuing. Secondly, the results from the filter simply reveal a total RCS mass estimate collected over the entire sampling period. The subsequently calculated mass per unit volume of air is therefore by necessity an average over the entire sampling period. This average may well hide so-called exceedances where the concentration of RCS in the air may, for short periods, be very much higher than safe limits of exposure.